Cross Reference to Related Applications
The present application is related to patent applications, Ser. Nos. 857,920, 857,921, 857,925, filed Dec. 6, 1977, for A. H. Bobeck.
Magnetic bubble memories are well known in the art. The most familiar mode of operating a magnetic bubble memory is termed the "field-access" mode. In this mode, a pattern of magnetically soft elements is formed in a plane adjacent a layer of material in which the bubbles are moved. A magnetic field is generated in the plane of bubble movement and caused to reorient to incrementally-offset radial positions (precess) cyclically in the plane. The pattern of elements is shaped so that various portions thereof respond to the in-plane field to generate pole patterns which move as the field precesses in a manner to cause bubble movement.
The most familiar pattern of elements includes T and bar shaped elements although many other element geometries such as asymmetric half discs also are being used presently. U.S. Pat. No. 3,534,347 of A. H. Bobeck, issued Oct. 13, 1970, discloses the basic field-access mode of operating magnetic bubble memories. The elements are formed from a layer of magnetically soft material such as permalloy. But, for example, ion-implanted regions, mesas and grooves in the bubble layer also operate in the field-access manner.
Because magnetic bubbles were becoming increasingly smaller and were being moved increasingly faster, as the art developed, detection of a bubble became the focus of attention fairly early in the development of the art. For the field-access mode of operating a bubble device, permalloy elements, operative in response to the reorienting in-plane field, were organized in groups to enlarge a bubble for detection. In this connection, increasing numbers of chevron-shaped elements were arranged in successive stages to elongate a bubble laterally with respect to the direction of bubble movement. The elements of the stage typically with the largest number of elements were interlinked by permalloy interlinking elements to form a magneto-resistance detector capable of detecting the presence and absence of a bubble during operation. U.S. Pat. No. 3,702,995 of A. H. Bobeck, F. J. Ciak, and W. Strauss, issued Nov. 14, 1972, discloses such an arrangement.
An alternative form of magnetic bubble memory employs electrical conductors for moving the bubbles. The conductors are formed in multiple layers, insulated from one another and driven in a three-phase manner. U.S. Pat. No. 3,460,116 of A. H. Bobeck, U. F. Gianola, R. C. Sherwood and W. Shockley, issued Aug. 5, 1969, discloses one such arrangement.
In such a "conductor-access" bubble memory, an elongated conductor loop is driven to cause enlargement of a bubble for detection. The bubble is usually detected, on collapse. R. F. Fischer, U.S. Pat. No. 3,564,518 issued Feb. 16, 1971, discloses such an arrangement.
A copending application of A. H. Bobeck, Ser. No. 857,921 filed on even date herewith, discloses a new and novel type of bubble memory with a conductor propagation arrangement where only a single electrically conducting implementation is employed. That is to say, the propagation arrangement for moving magnetic bubbles employs a single layer of electrically conducting material which includes an array of apertures and to which a single, multiphase pulse form is applied for effecting bubble movement.
A problem with such a conductor-access bubble memory is the detection of a bubble. There is no single electrical conductor loop present for expanding a bubble nor is there permalloy or an in-plane field for this purpose as is the case with field-access bubble memories.